It is clear that the whole world is passing through a social revolution in which a central _____ must be taken by scientists and technologists.
Everyone has periods in their lives ______ everything seems very hard.
.It will not be ________ we can meet again.
. He is a cutler(刀具商)--_____, a man who sells knives and sharp tools.
. He insisted that we ________ rest until we finish the work.
. I’ll never trust such a man ______ you described.